A light string is a string-shaped illumination device having a plurality of light sources (for example, light emitting diodes or small-sized bulbs) through serial connection, parallel connection or hybrid connection of serial/parallel connection. The number of light sources in the light string affects the optimized driving voltage of the light string. Taking a serial connection light string as an example, if all light sources need to reach a same luminance, a long light string needs a relatively large driving voltage, and a short light string needs a relatively small driving voltage. Therefore, an optimized driving circuit needs to be matched with the design of the light string, so that all light sources can reach a maximum luminance allowed by the specification (a maximum current that can be received), without burning out or failing.
When a light string device is assembled in a factory or a consumer replaces a light string of the light string illumination device, a correct model of light string corresponding to the driving circuit is required. Otherwise, the driving voltage may be excessively small to cause an insufficient luminance, or the driving voltage may be excessively large to cause the light string to burn out. For a manufacturer or a vendor, the need for multiple driving circuit models creates an inventory and stock management challenge.
Currently there are driving circuits that can change the output voltage. A user or an assembler has to switch the output voltages of these known driving circuits correctly by using a switch. If the output voltage is set incorrectly, for example, too high, the light string quickly burns out after being powered on.